1. Field of the Invention
The present invention relates to nozzles assemblies and more specifically to nozzle assemblies which enable quick and easy connection/disconnection in cramped and hazardous environments such as encountered in nuclear reactors.
2. Description of the Prior Art
It is essential that a hermetic, radiation proof, seal be maintained between the interior and exterior of a pressure vessel such as a nuclear reactor. It is also necessary to monitor the operations of a reactor using In-Core Instruments (ICI). However, this latter requirement necessitates the provision of nozzles through which the instruments can be sealingly introduced into the core. Examples of such arrangements are shown in U.S. Pat. No. 4,723,795 issued on Feb. 9, 1988 in the name of Shenoy and U.S. Pat. No. 4,655,483 issued on April 7, 1987 in the name of Margotta. These documents disclose techniques for providing fluid tight connections between a nozzle and a column which is concentrically supported within the nozzle.
FIG. 1 shows a less preferred embodiment of the type of nozzle to which the present invention pertains. This arrangement is such as to provide a fluid-tight, radiation proof, seal for a plurality of ICI (In Core Instruments) and allows the operative connection with external controls and monitoring arrangements.
This arrangement features the use of a GRAYLOC hub 10 which is clamped securely to a GRAYLOC flange 12 formed at the upper end of an ICI nozzle 14. However, with this arrangement when it is required to disassemble the same, the GRAYLOC clamp 16 is unbolted and each individual ICI nut 18 is then removed and the individual ICIs are then clustered together under a bullet nose. The above-mentioned GRAYLOC hub and GRAYLOC clamp are products of the Gray Tool Company, Houston, Texas.
FIGS. 7 and 8 are sectional views of the two main styles of conventional ICI flanges currently in use at nuclear power plants. Typically, there are 6 to 10 ICI flanges on the reactor vessel closure head, each of which houses up to six ICIs. FIG. 7 shows a standard bolted flange assembly 200 mounted to a closure head nozzle 201 of a reactor head. The standard bolted flange assembly 200 includes a mating flange 202 having a plurality of circumferentially-spaced holes for receiving nut and bolt assemblies 203. A flexitallic gasket 204 is fitted between the mating flange 202 and the closure head nozzle 201 to effect a fluid-tight, radiation proof seal. A plurality of ICI assemblies 205 are mounted to the mating flange 202 and secured in place with drive nuts 206. Gaskets 207 ensure a fluid and radiation tight seal between the ICI assemblies 205 and the mating flange 202.
During refueling and servicing of a reactor plant using the standard bolted flange assemblies 200, the nut and bolt assemblies 203 and each of the individual ICI nuts 206, along with the respective seals 204 and 207, must be removed. The ICI assemblies must be removed from the mating flange 202 regardless of whether the ICIs are scheduled to be replaced since the lower portions of the ICI assemblies 205 disposed within the pressure vessel remain in place while the closure head (not shown), along with the nozzles 201, is lifted off of the pressure vessel. The mating flange 202 is typically very heavy and unwieldy requiring two or more people to manipulate. Accordingly, this arrangement requires a significant amount of time and effort to disassemble and reassemble each time the head of the reactor is removed.
The other type of conventional flange assembly is the GRAYLOC flange assembly shown in FIG. 8. This assembly includes a GRAYLOC hub 210 positioned over the opening of the closure head nozzle 211. The closure head nozzle 211 includes a GRAYLOC flange 212 which is clamped securely to the hub 210 by a GRAYLOC clamp 213. A metal GRAYLOC seal ring 214 is positioned between the GRAYLOC flange 212 and the hub 210. The GRAYLOC clamp 213 includes a pair of large matching clamshell clamps secured together with four stud and nut sets inserted through holes 215. The ICI assemblies 216 are secured to the GRAYLOC hub 210 by drive nuts 217 and are sealed against leakage by GRAFOIL gaskets 218 which are compressed by torquing the drive nuts 217 to a high value.
During refueling and servicing of a reactor with the conventional GRAYLOC flange assembly, it is necessary to unbolt and remove the GRAYLOC clamps 213 prior to lifting the ICI assembly from the closure head nozzle 211. As with the embodiment of FIG. 7, each of the individual ICI nuts 217, along with the seals 218, are removed from the hub 210 regardless of whether the ICIs are scheduled to be replaced. The GRAYLOC hub 210 and clamps 213 are quite heavy and difficult to maneuver over the comparatively delicate instrumentation. This operation requires two or more people to complete. The clamps and stud and nut sets require a significant amount of work to manipulate, and the drive nuts 217 at each of the ICI locations require substantial torque to effect a seal.
The above-described conventional flange assemblies have significant drawbacks in that the disassembly process is both labor intensive and time consuming. The disassembly process is especially tedious because it is carried out in very cramped conditions and in a radioactive environment. Accordingly, the operators are required to wear protective suiting and must be careful to monitor the amount of time for which they are exposed to the radiation.
Therefore, there is a need for an arrangement which can reduce both the effort and time required to achieve the disassembly of an ICI nozzle which is carried out each time a refueling or instrument change is required, in order to reduce the reactor down time and, more importantly, to reduce the health risks associated with working in the above mentioned hazardous environment.